The present invention relates generally to methods for fabricating fiber-metal matrix composites and more particularly to an improved method for laying up fiber and metal matrix material for improved structural strength in the composite.
Conventional continuous fiber metal matrix composites may be produced in alternate layers of ceramic fiber mats and metal foil which are encapsulated, outgassed and consolidated by hot pressing. In order to hold the fibers in place during processing, fiber mats are produced by interweaving strands of metallic crossweave material, usually wire (typically about 2 mils dia) or ribbon (typically 5-10 mils wide by 1/2-2 mils thick), in a box weave pattern of alternate fibers (typically 4-6 mils dia) and crossweave strands, the crossweave strands typically being spaced apart about 18 to 35 fiber diameters. However, because of the tension in the crossweave strands, such as might be imposed on the strands incident to the weaving process, the fibers are displaced out of the plane of the centerline of the fabric and are bent into wave-like patterns of undulations over and under the crossweave strands, the undulations lying in planes perpendicular to the centerline plane of the fabric. When the fiber mat is pressed between foil during processing, the fibers rotate and buckle and may break the crossweave strands and tend to slide along the crossweave strands so that large arcs are formed defining defect areas in the ply which are devoid of fibers and wherein the fibers are not parallel to the design lead axis.
The invention solves or substantially reduces in critical importance problems with conventional composite fabrication methods by providing an improved method for laying up the composite which eliminates the problem of fiber bow in the mats by placing the crossweave strands close together in sets of two or more. The crossweave strands are crimped around and against each fiber, which crimping of the strands holds each fiber tightly in place and prevents the fibers from slipping along the crossweave. As a result, the fibers lie flat in or very near the plane of the centerline of the mat. Geometrical instability and defects resulting from fiber bowing in the finished composite are substantially eliminated.
It is therefore a principal object of the invention to provide a method for fabricating fiber-metal matrix composites.
It is a further object of the invention to provide a method for fabricating a fiber-metal matrix composite having enhanced strength.
It is yet another object of the invention to provide a method for fabricating a fiber-metal matrix composite free of certain defects.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.